The pre-dialysis serum sodium (Na+) concentration is relatively constant in hemodialysis patients, but varies with each patient's individual osmolar set point. See F. M. De Paula, et al., Clinical consequences of an individualized dialysate sodium prescription in hemodialysis patients, Kidney International, Vol. 66 (2004) pp. 1232-1238; A. S. Peixoto, et al., Long-Term Stability of Serum Sodium in Hemodialysis Patients, Blood Purification, Vol. 29 (2010) pp. 264-267, and M. L. Keen, and F. A. Gatch, The association of the sodium “setpoint” to interdialytic weight gain and blood pressure in hemodialysis patients, The International Journal of Artificial Organs, Vol. (11) pp. 971-979 (2007). The gradient (GNa+) between the serum sodium (SNa+) concentration and the dialysate sodium (DNa+) concentration is a major determinant of post-dialytic SNa+ concentration. A positive gradient (DNa+>SNa+) can result in a higher post-dialytic SNa+, and consequent thirst, excess interdialytic weight gain, volume overload, and increased blood pressure. A negative gradient (DNa+<SNa<+) is also undesirable because it can result in the patient becoming hypotensive. Basing DNa+ on SNa+ (e.g., gradient GNa+=0) would minimize diffusive sodium transport, and thus reduce the aforementioned problems. However, the measurement of the serum sodium concentration, SNa+measured, of each patient before each dialysis treatment is costly and time consuming using existing technology.
Therefore, there is a need for a method of controlling diffusive sodium transport from the dialysate solution to the blood of a patient undergoing dialysis treatment that minimizes or eliminates the aforementioned problems.